An economizer is normally employed to increase the capacity of refrigeration or air conditioning systems. The compressor discharge pressure varies seasonally and the saturated condensing temperature can drop too low. Under these circumstances the advantages of economizer operation is minimal. In two-stage compressor systems employing an economizer, injection normally takes place between the stages such that economizer gas mixes with the high stage suction gas supplied to the high stage. The economizer provides subcooling of the liquid and desuperheating of some vapor which results in a more efficient system. However, as the load requirements change, either only the high stage, or only the low stage may be used thereby obviating the benefits of supplying economizer gas to the suction of the high side.